A warning

This snapshot should be considered "extremely, extremely experimental". From a scale of 1-10 where 1 is experimental and 10 is stable, this is a very firm negative 5.

Back up your worlds before trying them in this snapshot. Don't expect worlds played in this snapshot to work in future snapshots.

But seriously

This snapshot represents a few years worth of internal refactoring to allow us to have virtually unlimited block & item IDs. But we fully expect everything to break. Please make backups.

Resource packs?

Are all broken by this too, sorry.

Install the snapshot

Please report any and all bugs you find in Minecraft to bugs.mojang.com. If nobody reports a bug, we can't fix it!

To get snapshots, open your launcher and go to the "launch options" tab. Check the box saying "Enable snapshots" and save. To switch between the snapshot and normal version, you can find a new dropdow menu next to the "Play" button. Back up your world first or run the game on in a different folder (In the "launch options" page).

Snapshots can corrupt your world, please backup and/or run them in a different folder from your main worlds.